T cells are thymus-derived cells in the immune system which mediate cellular immune reactions and regulate immune response. T lymphocytes (T cells) are divided into two subgroups by their usage of T cell receptors. About 90-98% of T cells have a.beta. receptors (a.beta. T cells) which recognize antigenic peptides bound to major histo-compatibility complex I or II molecules. About 2-10% of T cells have .gamma..delta. receptors (.gamma..delta. T cells).
A major human .gamma..delta. T cell subset expressing V.gamma.2 and V.delta.2 germlines (i.e. V.gamma.2V.delta.2 T cells) is found in human mycobacterial lesions (Modlin, R. L., et al. Nature 339:544-548 (1989)). V.gamma.2V.delta.2 T cells have been shown to expand acutely in response to mycobacterial pathogens such as M. tuberculosis and M. luprae, bacterial pathogens such as Gram-positive and Gram-negative bacteria, as well as parasites such as Plasmodium vivax (Kabelitz, D., et al. J. Exp. Med. 171:667-679 (1990); Panchamoorthy, G., et al. J. Immunol. 147:3360-3369 (1991); De Libero, G., et al. J. Exp. Med. 173:1311-1322 (1991); Hara, T., et al. J. Clin. Invest. 90:204-210 (1992); Goerlich, R., et al. Eur. J. Immunol. 21:2613-2616 (1991); and Goodier, M., et al. Int. Immunol. 4:33-41 (1992)). In addition, certain hematopoietic tumor cell lines such as Daudi and RPMI 8226 are specifically recognized and lysed by V.gamma.2V.delta.2 T cells (Fisch, P., et al. Science 250:1269-1273 (1990); Selin, L. K., et al. Scand. J. Immunol. 36:107-117 (1992)).
Because V.gamma.2V.delta.2 T cells recognize antigens which are expressed by a variety of diseases in humans, there exists a need to selectively stimulate the proliferation of V.gamma.2V.delta.2 T cells to enhance the immune response against these diseases. The present invention satisfies this need.